Apparatus and method for synchronizing and obtaining system information in wireless communication system

ABSTRACT

A base station and terminal use methods of obtaining synchronization and system information in a wireless communication system. An operation of a base station includes generating a synchronization signal to be transmitted through a Synchronization Channel (SCH), generating a broadcast signal to be transmitted through a Broadcast Channel (BCH), and transmitting repetitively the SCH and the BCH by performing beamforming on the channels with different transmission beams.

CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY

The present application is related to and claims the benefit under 35U.S.C. §119(a) of a Korean patent application filed in the KoreanIntellectual Property Office on Sep. 9, 2011 and assigned Serial No.10-2011-0091913, the entire disclosure of which is hereby incorporatedby reference.

TECHNICAL FIELD OF THE INVENTION

The present disclosure relates to a wireless communication system.

BACKGROUND OF THE INVENTION

In order to satisfy increasing demands on wireless data traffic,wireless communication systems are under development that support higherdata transfer rates. Techniques of 4^(th) Generation (4G) systems, whichare now being commercialized, are being developed to improve spectralefficiency in general to increase the data transfer rate. However, thetechniques of improving the spectral efficiency are not enough tosatisfy the explosively increasing demands on the wireless data traffic.

In one method of solving the aforementioned problem, a significantlywide frequency band is used. A frequency band used in a conventionalmobile communication cellular system at present is less than or equal to10 GigaHertz (GHz) in general, and thus it is very difficult to ensure awide frequency band. Therefore, there is a need to ensure a widebandfrequency in a higher frequency band. However, the higher the frequencyfor wireless communication, the greater the propagation path loss.Accordingly, a propagation distance is relatively short, which resultsin a coverage decrease. As a method of solving this problem, beamformingtechniques are used to decrease the propagation path loss and toincrease the propagation distance.

Beamforming can be classified into Transmission (TX) beamformingperformed in a transmitting end and reception (RX) beamforming performedin a receiving end. In general, the TX beamforming increases directivityby allowing an area in which propagation reaches to be densely locatedin a specific direction by using a plurality of antennas. In thissituation, aggregation of the plurality of antennas can be referred toas an antenna array, and each antenna included in the array can bereferred to as an array element. The antenna array can be configured invarious forms such as a linear array, a planar array, etc. The use ofthe TX beamforming results in the increase in the directivity of asignal, thereby increasing a propagation distance. Further, since thesignal is almost not transmitted in a direction other than a directivitydirection, a signal interference acting on another receiving end issignificantly decreased. The receiving end can perform beamforming on aRX signal by using a RX antenna array. The RX beamforming decreases theRX signal strength transmitted in a specific direction by allowingpropagation to be concentrated in a specific direction, and excludes asignal transmitted in a direction other than the specific direction fromthe RX signal, thereby providing an effect of blocking an interferencesignal.

As described above, in order to promote wide frequency bands, asuper-high frequency band, in other words, millimeter (mm) wave system,may be introduced. In this situation, a beamforming technique is takeninto consideration to overcome the propagation path loss. In thistechnique, a signal subjected to beamforming is transmitted and receivedstarting from an initial access time point. Accordingly, there is a needfor a method in which a user terminal obtains synchronization and systeminformation in an environment where beamforming is performed.

SUMMARY OF THE INVENTION

To address the above-discussed deficiencies of the prior art, it is aprimary object to provide at least the advantages described below.Accordingly, an aspect of the present disclosure is to provide anapparatus and method for obtaining synchronization by using aSynchronization Channel (SCH) subjected to beamforming in a wirelesscommunication system.

Another aspect of the present disclosure is to provide an apparatus andmethod for obtaining system information from a Broadcast Channel (BCH)subjected to beamforming in a wireless communication system.

Another aspect of the present disclosure is to provide an apparatus andmethod for determining a preferred transmission beam and a preferredreception beam by using a SCH.

Another aspect of the present disclosure is to provide an apparatus andmethod for obtaining frame synchronization by using system informationin a wireless communication system.

In accordance with an aspect of the present disclosure, a method ofoperating a base station in a wireless communication system is provided.The method includes generating a synchronization signal to betransmitted through a SCH, generating a broadcast signal to betransmitted through a BCH, and transmitting repetitively the SCH and theBCH by performing beamforming on the channels with differenttransmission beams.

In accordance with another aspect of the present disclosure, a method ofoperating a terminal in a wireless communication system is provided. Themethod includes detecting at least one of SCHs repetitively transmittedby being beam-formed with different transmission beams, and obtainingsystem information by using at least one of BCHs repetitivelytransmitted by being beam-formed with different transmission beams.

In accordance with another aspect of the present disclosure, a basestation apparatus in a wireless communication system is provided. Theapparatus includes a modem configured to generate a synchronizationsignal to be transmitted through a SCH and generate a broadcast signalto be transmitted through a BCH. The apparatus also includes abeamforming unit configured to perform beamforming on the SCH and theBCH with different transmission beams. The apparatus further includes acontroller configured to transmit repetitively the SCH and the BCH whichare beam-formed with the different transmission beams.

In accordance with another aspect of the present disclosure, a terminalapparatus in a wireless communication system is provided. The apparatusincludes a modem configured to detect at least one of SCHs repetitivelytransmitted by being beam-formed with different transmission beams. Theapparatus also includes a controller configured to obtain systeminformation by using at least one of BCHs repetitively transmitted bybeing beam-formed with different transmission beams.

Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, itmay be advantageous to set forth definitions of certain words andphrases used throughout this patent document: the terms “include” and“comprise,” as well as derivatives thereof, mean inclusion withoutlimitation; the term “or,” is inclusive, meaning and/or; the phrases“associated with” and “associated therewith,” as well as derivativesthereof, may mean to include, be included within, interconnect with,contain, be contained within, connect to or with, couple to or with, becommunicable with, cooperate with, interleave, juxtapose, be proximateto, be bound to or with, have, have a property of, or the like; and theterm “controller” means any device, system or part thereof that controlsat least one operation, such a device may be implemented in hardware,firmware or software, or some combination of at least two of the same.It should be noted that the functionality associated with any particularcontroller may be centralized or distributed, whether locally orremotely. Definitions for certain words and phrases are providedthroughout this patent document, those of ordinary skill in the artshould understand that in many, if not most instances, such definitionsapply to prior, as well as future uses of such defined words andphrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and itsadvantages, reference is now made to the following description taken inconjunction with the accompanying drawings, in which like referencenumerals represent like parts:

FIGS. 1A and 1B illustrate an example of a cell structure in a wirelesscommunication system according to an embodiment of the presentdisclosure;

FIG. 2 illustrates an example structure of a Synchronization Channel(SCH) and a Broadcast Channel (BCH) in a wireless communication systemaccording to an embodiment of the present disclosure;

FIG. 3 illustrates a method of determining a reception beam by using aSCH in a wireless communication system according to an embodiment of thepresent disclosure;

FIG. 4 is a flowchart illustrating an operation of a base station in awireless communication system according to an embodiment of the presentdisclosure;

FIG. 5 is a flowchart illustrating an operation of a terminal in awireless communication system according to an embodiment of the presentdisclosure;

FIG. 6 is a block diagram illustrating a structure of a base station ina wireless communication system according to an embodiment of thepresent disclosure; and

FIG. 7 is a block diagram illustrating a structure of a terminal in awireless communication system according to an embodiment of the presentdisclosure.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1A through 7, discussed below, and the various embodiments used todescribe the principles of the present disclosure in this patentdocument are by way of illustration only and should not be construed inany way to limit the scope of the disclosure. Those skilled in the artwill understand that the principles of the present disclosure may beimplemented in any suitably arranged wireless network.

The present disclosure relates to an apparatus and method forsynchronizing and obtaining system information in the wirelesscommunication system. The present disclosure described hereinafterrelates to a technique for obtaining, synchronization from aSynchronization Channel (SCH) subjected to beamforming and for obtainingsystem information from a Broadcast Channel (BCH) in a wirelesscommunication system.

The SCH is a resource period for delivering a synchronization signal forobtaining time/frequency synchronization of a terminal, and has apre-set fixed position on a frame. The synchronization signal consistsof a pre-agreed sequence, and can also be referred to as a preamble, amidamble, etc. In the following description, remarks such as “a SCH istransmitted/received”, “a synchronization signal istransmitted/received”, and the like, are used for the same meaning.

The BCH is a resource period for delivering system information used toaccess and communicate with a system, and has a pre-set fixed positionon the frame. The BCH can also be referred to as a frame header, asuperframe header, etc. In the following description, remarks such as “aBCH is transmitted/received”, “a broadcast signal istransmitted/received”, “system information is transmitted/received” orthe like are used for the same meaning.

In general, a mobile communication system adopts the concept of a“cell”. Accordingly, a handover process is performed when a terminalmoves from one cell to another cell. Although it may differ depending onsystem characteristics, one Base Station (BS) generally forms aplurality of sectors by using a plurality of sector antennas. Inaddition, an “antenna area” is defined in the present disclosure assubordinated concept of the cell. The antenna area is a regional unit inwhich beamforming is performed. In one cell, antenna areas aredistinguished by antenna identifiers (IDs). A beam index allocated toeach TX beam is unique in one antenna area. For each antenna area, atleast one Radio Frequency (RF) chain and antenna area can be allocated,or antenna elements belonging to one antenna array can be allocated in adivided manner. Hereinafter, for convenience of explanation, a group ofat least one antenna for one antenna area is called an ‘antenna group’.That is, one antenna group is allocated to one antenna area. Antennagroups can be arranged physically in the same space or in separatespaces.

FIGS. 1A and 1B illustrate an example of a cell structure in a wirelesscommunication system according to an embodiment of the presentdisclosure. FIG. 1A illustrates a structure where each cell has oneantenna area, and FIG. 1B illustrates a structure where each cell hastwo antenna areas. Referring to FIGS. 1A and 1B, a BS operates threecells, and each antenna area supports three TX beams. When transmittinga SCH or a BCH, as shown in FIG. 1A, the BS changes a TX beam in onecell and transmits three signals across three unit-time periods.Alternatively, as shown in FIG. 1B, the BS can change a TX beam in onecell and transmit six signals across three unit-time periods. That is,since two signals belonging to different antenna areas are spatiallymultiplexed in the embodiment shown in FIG. 1B, the BS cansimultaneously transmit signals in an antenna area-0 and an antennaarea-1 by using different antenna groups.

If each antenna area has the same number of TX beams, the greater thenumber of antenna areas, the more efficiently the communication can beperformed by the system by using narrow beams. Alternatively, if eachcell has the same number of TX beams, the greater the number of antennaareas, the less the resource amount required by the system fortransmission of the SCH and the BCH. Although it is described in FIGS.1A and 1B that each antenna area has three TX beams, according toanother embodiment of the present disclosure, four or more TX beamshaving a narrower beam width can be used.

FIG. 2 illustrates an example structure of a SCH and a BCH in a wirelesscommunication system according, to an embodiment of the presentdisclosure. It is assumed in FIG. 2 that five TX beams are supported.

Referring to FIG. 2, a frame 210 includes a plurality of subframes 220.The subframe 220 is divided into a DownLink (DL) period 232 and anUpLink (UL) period 234. Although the DL period 232 and the UL period 234are divided in a time axis in FIG. 2, according to another embodiment ofthe present disclosure, the DL period 232 and the UL period 234 can bedivided in a frequency axis. Some parts of the DL period 232 are definedas a SCH/BCH period 240. The SCH/BCH period 240 is includedperiodically. In the embodiment of FIG. 2, the SCH/BCH period exists inevery frame.

The SCH/BCH period 240 is located at a rear part of the DL period 232.That is, a last symbol of a BCH-4 264 located at a rearmost part of theSCH/BCH period 240 is a last symbol of the DL period 232. Therefore,synchronization of the frame 210 can be obtained by determining aposition of the last BCH 264. However, according to another embodimentof the present disclosure, the SCH/BCH period 240 can be arranged in thesubframe 220 or the frame 210 in a distributed manner, or can be locatedin a front or middle part of the DL period 232 instead of being locatedin the rear part thereof. In addition, according to another embodimentof the present disclosure, the SCH/BCH period 240 included in one DLperiod 232 may be plural in number.

The SCH/BCH period 240 includes a plurality of SCHs 250-254 and aplurality of BCHs 260-264. One SCH and one BCH are paired to each other.The SCH and BCH included in one pair are beam-formed with a TX beam inthe same direction. That is, a SCH-0 250 and a BCH-0 260 are beam-formedin a TX beam in the same direction. Further, five SCH/BCH pairs includedin one frame 210 are beam-formed with a TX beam in different directions.The number of SCH/BCH pairs can vary depending on the number of TX beamssupported by a BS. In FIG. 2, one SCH and one BCH which are paired toeach other are adjacent in a time axis. However, according to anotherembodiment of the present disclosure, the SCH and the BCH which arepaired to each other can be spaced apart from each other by a length ofa pre-set number of symbols. For example, the plurality of SCHs 250-254can be contiguously arranged, and the plurality of BCHs 260-264 can becontiguously arranged. In addition, according to another embodiment ofthe present disclosure, the plurality of SCHs 250-254 can consist of twosymbols respectively distinguished as a primary SCH and a secondary SCH.

Synchronization signals transmitted through the SCHs 250-254 indicatecell IDs. Further, if there are a plurality of antenna areas as shown inFIG. 1B, the synchronization signals can further indicate antenna areaIDs. The cell ID and the antenna area ID can be indicated by using atleast one of a sequence constituting the synchronization signal, aposition of a subcarrier to which the synchronization signal is mapped,a scrambling code for the synchronization signal, and a covering code.

In addition, the SCHs 250-254 deliver synchronization signals which arebeam-formed by using different TX beams, and the different TX beams areidentified by using beam IDs. According to one embodiment of the presentdisclosure, the beam IDs can be indicated by using the SCHs 250-254. Forexample, the beam ID can be indicated by using at least one of asequence constituting the synchronization signal, a position of asubcarrier to which the synchronization signal is mapped, a scramblingcode for the synchronization signal, and a covering code. According toanother embodiment of the present disclosure, the beam ID can beincluded in system information transmitted through the BCHs 260-264. Inthis situation, a beam ID of a TX beam applied to the SCH-0 250 isincluded in the system information transmitted through the BCH-0 260. Ifthe beam ID is transmitted through the BCHs 260-264, a synchronizationsignal has a relatively simple structure, and thus a process ofobtaining synchronization becomes simple and clear. Otherwise, if thebeam ID is indicated through the SCHs 250-254, the same systeminformation is transmitted through all of the BCHs 260-264. In thissituation, since the same physical signal is generated from the systeminformation, the terminal can obtain a decoding gain by combiningsignals received through the BCHs 260-264. However, even if the beam IDis transmitted through the BCHs 260-264, when the beam ID is used as ascrambling code of the system information rather than one informationitem of the system information, the terminal can increase the decodinggain by combining the signals after performing descrambling.

To obtain frame synchronization of the terminal, the system informationincludes information capable of determining, a boundary of the SCH/BCHperiod 240. The SCH/BCH period 240 has a fixed position in the frame.Therefore, when the position of the SCH/BCH period 240 can be known, theterminal can determine the boundary of the frame. The terminal candetect at least one of the SCHs 250 to 254 which are beam-formed withdifferent TX beams. However, one SCH is not enough to correctly know theboundary of the SCH/BCH period 240. This is because the terminal cannotknow the number of SCHs other than the SCH detected by the terminalitself. Therefore, after determining the number of SCHs by using thesystem information, in other words, after determining the number of TXbeams supported by the BS, the terminal can determine the number of SCHsother than the SCH detected by the terminal itself by using the numberof TX beams, and can determine the boundary of the SCH/BCH period 240.For example, as shown in FIG. 2, if the last symbol of the SCH/BCHperiod 240 is the last symbol of the DL period 232, the terminal thatdetects the SCH-2 252 confirms that the number of TX beams is five byusing the system information, and determines that two more SCHs arepresent subsequently to the SCH-2 252. Accordingly, the terminal candetermine a last symbol position of the SCH/BCH period 240, and candetermine an end boundary of the DL period 232. If a positional relationbetween the SCH/BCH period 240 and the boundary of the subframe 220 isnot pre-set, the positional relation between the SCH/BCH period 240 andthe boundary of the subframe 220 can be delivered by using the systeminformation.

It is illustrated in FIG. 2 that one DL period 232 and one UL period 234are included in the range of the subframe 220, and a group of aplurality of subframes 220 corresponds to the frame 210. However,according to another embodiment of the present disclosure, the subframe220 can be called a frame, and the frame 210 can be called a superframe.

FIG. 3 illustrates a method of determining a RX beam by using a SCH in awireless communication system according to an embodiment of the presentdisclosure. It is assumed in FIG. 3 that a BS supports four TX beams,and a terminal supports four RX beams.

Referring to FIG. 3, the BS periodically transmits SCHs in every frame.That is, each frame includes one TX period of the SCH. In thissituation, during one frame, the BS applies beamforming to the SCHs byusing supportable TX beams. In other words, the BS transmits the SCHfour times in every frame, and four SCHs are beam-formed with a TX beamA 311, a TX beam B 312, a TX beam C 313, and a TX beam D 314.

Accordingly, the terminal changes a RX beam in every frame and receivesthe SCHs across a plurality of frames. For one example, if the terminalhas only one RX RF chain, the terminal performs beamforming by using oneRX beam in every frame, and receives the SCHs only during four frames.That is, as shown in FIG. 3, the terminal performs RX beamforming byusing the RX beam A 321 in a frame n, the RX beam B 322 in a frame n+1,the RX beam C 323 in a frame n+2, and the RX beam D 324 in a frame n+3.For another example, if the terminal has two RX chains, the terminalperforms beamforming in every frame by using two RX beams, and receivesthe SCHs during two frames. That is, as shown in FIG. 3, the terminalperforms RX beamforming by using the RX beam A 321 and the RX beam B 322in the frame n, and the RX beam C 323 and the RX beam D 324 in the framen+1.

By using the aforementioned process, the terminal receives the SCHs bycombining all TX beams and RX beams. Accordingly, the terminal candetermine one combination which maximizes RX signal strength as anoptimal TX beam and an optimal RX beam.

A beam width of a TX beam used in the BS is not limited in theembodiment of FIG. 3. However, according to another embodiment of thepresent disclosure, the terminal can determine the optimal TX beam byusing TX beams having different beam widths in a stepwise manner.

Hereinafter, an operation and structure of a terminal and a BS which usea SCH and a BCH having the aforementioned structure will be described indetail with reference to the accompanying drawings.

FIG. 4 is a flowchart illustrating an operation of a BS in a wirelesscommunication system according to an embodiment of the presentdisclosure.

Referring to FIG. 4, the BS generates a synchronization signal in block401. The synchronization signal is a signal that includes a pre-setsequence transmitted through a SCH. The synchronization signal indicatesa cell ID. When the BS operates a plurality of antenna areas in onecell, the synchronization signal further indicates an antenna area ID.In this situation, the BS generates different synchronization signalsfor respective antenna areas. In addition, according to one embodimentof the present disclosure, the synchronization signals can indicate TXbeam IDs to be applied. In this situation, the BS generates differentsynchronization signals for respective TX beams to be applied. The cellID, the antenna area ID, and the TX beam ID can be indicated by using atleast one of a sequence constituting the synchronization signal, aposition of a subcarrier to which the synchronization signal is mapped,a scrambling code for the synchronization signal, a covering code, etc.According to another embodiment of the present disclosure, the TX beamID can be indicated through a BCH, and in this situation, thesynchronization signals do not indicate the TX beam IDs to be applied.

In block 403, the BS encodes system information. In other words, the BSgenerates a broadcast signal to be transmitted through the BCH. Thesystem information includes configuration information, systemparameters, etc., used by the terminal to access the BS. For example,the system information can include information for reporting the numberof TX beams supported by the BS, information capable of determining aboundary of a SCH/BCH period, etc. If the position of the boundary ofthe SCH/BCH period on the frame is not pre-set, the system informationmay further include information for reporting the position of theboundary of the SCH/BCH period on the frame. According to one embodimentof the present disclosure, if the TX beam ID is indicated by the SCH,the broadcast signal is not different for each TX beam but is identicalfor each TX beam. Alternatively, according to another embodiment of thepresent disclosure, if the TX beam ID is indicated through the BCH, thebroadcast signal is different for each TX beam. Specifically, the TXbeam ID may be included as one information item of the systeminformation, or may be indicated in a form of a scrambling applied tothe system information.

In block 405, the BS repetitively transmits the synchronization signaland the broadcast signal by performing beamforming on the signals byusing different TX beams. In other words, during one SCH/BCH period, theBS transmits SCHs and BCHs which are beam-formed with different TXbeams. Accordingly, one SCH/BCH period includes pairs of the SCH and theBCH by the number of TX beams supported by the BS. In this situation,when the BS operates a plurality of antenna areas in one cell, the BStransmits simultaneously the SCH and the BCH in the antenna areas. Thatis, since the antenna areas can be independently beam-formed, the BSforms one TX beam per antenna area, that is, forms simultaneously TXbeams by the number of antenna areas.

In block 407, the BS determines whether a TX period of the SCH/BCH isover. For example, the TX period of the SCH/BCH may be a subframe, aframe, or a superframe. That is, the SCH/BCH period is periodicallyarranged, and has a fixed position in the frame. When the TX period ofthe SCH/BCH is over, the procedure returns to block 401. However,according to another embodiment of the present disclosure, thepreviously generated synchronization signal and broadcast signal may bereused. In this situation, the procedure returns to block 405.

Although not shown in FIG. 4, the BS may further perform a process ofreceiving a feedback of a preferred TX beam ID from the terminal whichreceives the SCH and the BCH. In this situation, the BS recognizes apreferred TX beam of the terminal, and uses the preferred TX beam of theterminal when performing scheduling.

FIG. 5 is a flowchart illustrating an operation of a terminal in awireless communication system according to an embodiment of the presentdisclosure.

Referring to FIG. 5, the terminal determines a preferred TX beam and apreferred RX beam by using SCHs in block 501. The SCHs are periodicallytransmitted, and during one period, SCHs beam-formed with different TXbeams are repetitively transmitted. For example, a TX period of the SCHmay be a frame or a superframe. Therefore, since the terminal changes aRX beam in every period during a plurality of periods and receives theSCHs, the terminal can receive the SCHs by combining all of TX beams andRX beams. Accordingly, the terminal can determine one combination whichmaximizes RX signal strength as the preferred TX beam and the preferredRX beam. In this situation, the number of RX beams that can besimultaneously applied by the terminal may vary depending on the numberof RX RF chains included in the terminal.

In block 503, the terminal obtains at least one of a cell ID, an antennaarea ID, and a TX beam ID by using the SCHs. A synchronization signalreceived through the SCH indicates the cell ID. When the BS operates aplurality of antenna areas in one cell, the synchronization signalfurther indicates the antenna area ID. In addition, according to oneembodiment of the present disclosure, the synchronization signals mayindicate TX beam IDs. The cell ID, the antenna area ID, and the TX beamID can be indicated by using at least one of a sequence constituting thesynchronization signal, a position of a subcarrier to which thesynchronization signal is mapped, a scrambling code for thesynchronization signal, a covering code, etc. That is, the terminal canidentify at least one of the cell ID, the antenna area ID, and the TXbeam ID by using at least one of the sequence of the detectedsynchronization signal, the position of the subcarrier to which thesynchronization signal is mapped, the scrambling code for the detectedsynchronization signal, the covering code, etc. According to anotherembodiment of the present disclosure, the TX beam ID can be indicated byusing the BCH. In this situation, the synchronization signals do notindicate the TX beam ID to be applied.

In block 505, the terminal decodes the BCH. The BCH is paired with theSCH. The BCH is beam-formed with the same TX beam as the SCH paired withthe BCH. The BCH is spaced apart from the SCH which is paired with theBCH by a distance corresponding to the pre-set number of symbols. Forexample, as shown in FIG. 2, the SCH and the BCH which are paired toeach other can be arranged in a contiguous manner. Therefore, theterminal which detects the synchronization signal can determine aposition of a BCH beam-formed with the same TX beam from thesynchronization signal. In this situation, the terminal can apply thepreferred RX beam determined in block 501 to the BCH. The BCH deliverssystem information. The system information includes configurationinformation, system parameters, etc., used by the terminal to access theBS. According to one embodiment of the present disclosure, if the TXbeam ID is indicated by the SCH, the broadcast signal is not differentfor each TX beam but is identical for each TX beam. Therefore, theterminal can increase a decoding gain by combining a plurality ofbroadcast signals. Alternatively, according to another embodiment of thepresent disclosure, if the TX beam ID is indicated through the BCH, thebroadcast signal is different for each TX beam. Specifically, the TXbeam ID may be included as one information item of the systeminformation, or may be indicated in a form of a scrambling applied tothe system information. When the TX beam ID is indicated in a form of ascrambling code, the terminal can increase a decoding gain by combininga plurality of broadcast signals after performing descrambling.

In block 507, the terminal obtains frame synchronization. That is, theterminal determines a boundary of a superframe, a frame, a subframe,etc., by using system information obtained through the BCH and aposition of the detected synchronization signal. That is, the terminaldetermines a boundary of a SCH/BCH period by using the systeminformation, and determines a boundary of the frame from the boundary ofthe SCH/BCH period. For example, if an end boundary of the SCH/BCHperiod has a fixed position in the frame, the terminal determines thenumber of SCHs by using the system information, calculates the number ofSCHs located subsequent to the SCH detected by the terminal, determinesthe end boundary of the SCH/BCH period, and determines the boundary ofthe frame according to a positional relation of the end boundary and theframe. In this situation, if the position of the boundary of the SCH/BCHperiod on the frame is not pre-set, the terminal can obtain informationfor reporting the position of the boundary of the SCH/BCH period on theframe by using the system information.

Although not shown in FIG. 5, the terminal can further perform a processof feeding back a TX beam ID of the preferred TX beam determined inblock 501.

FIG. 6 is a block diagram illustrating a structure of a BS in a wirelesscommunication system according to an embodiment of the presentdisclosure.

Referring to FIG. 6, the BS includes a modem 610, a receiver 620, a TXRF chain 630, a beamforming unit 640, an antenna array 650, and acontroller 660.

The modem 610 performs a conversion function between a baseband signaland a bit-stream according to a physical layer standard of the system.For example, in an OFDM scheme, in a data transmission process, themodem 610 generates complex symbols by performing coding and modulationon a TX bit-stream, maps the complex symbols to subcarriers, and thenconfigures OFDM symbols by performing an Inverse Fast Fourier Transform(IFFT) operation and a Cyclic Prefix (CP) insertion operation. Inaddition, in a data reception process, the modem 610 splits the basebandsignal on an OFDM symbol basis, restores signals mapped to thesubcarriers by using a Fast Fourier Transform (FFT) operation, and thenrestores a RX bit-stream by performing demodulation and decoding. Thereceiver 620 converts an RF signal received from the terminal into abaseband digital signal. Although not shown specifically, the receiver620 includes an antenna, a RX RF chain, etc.

The TX RF chain 630 converts a baseband digital signal stream providedfrom the modem 610 into an RF analog signal. For example, the TX RFchain 630 can include an amplifier, a mixer, an oscillator, a Digital toAnalog Converter (DAC), a filter, etc. Only one TX RF chain 630 isillustrated in FIG. 6. However, according to another embodiment of thepresent disclosure, the BS can include a plurality of TX RF chains. Inthis situation, the BS can simultaneously form a plurality of TX beamsby the number of TX RF chains.

The beamforming unit 640 performs TX beamforming on a TX signal providedfrom the TX RF chain 630. For example, the beamforming unit 640 includesa plurality of phase converters, a plurality of amplifiers, and a signaladder. That is, the beamforming unit 640 splits the TX signal providedfrom the TX RF chain 630 by the number of the plurality of antennasincluded in the antenna array 650, and regulates a phase and size ofeach of the split signals. The antenna array 650 is a group of aplurality of antennas. The antenna array 650 includes a plurality ofarray elements, and transmits signals provided from the beamforming unit640 through a radio channel.

The controller 660 controls an overall function of the BS. For example,the controller 660 generates a TX traffic packet and message andprovides it to the modem 610, and interprets a RX traffic packet andmessage provided from the modem 610. In particular, the controller 660provides control to transmit a SCH and a BCH according to one embodimentof the present disclosure. An operation of the controller 660 fortransmitting the SCH and the BCH will be described below.

The controller 660 controls the modem 610 to determine a sequence of asynchronization signal and to generate the synchronization signal bydemodulating the sequence. The synchronization signal indicates a cellID. When the BS operates a plurality of antenna areas in one cell, thesynchronization signal further indicates an antenna area ID. In thissituation, the controller 660 generates different synchronizationsignals for respective antenna areas. In addition, according to oneembodiment of the present disclosure, the synchronization signals canindicate TX beam IDs to be applied. In this situation, the controller660 generates different synchronization signals for respective TX beamsto be applied. The cell ID, the antenna area ID, and the TX beam ID canbe indicated by using at least one of a sequence constituting thesynchronization signal, a position of a subcarrier to which thesynchronization signal is mapped, a scrambling code for thesynchronization signal, a covering code, etc. According to anotherembodiment of the present disclosure, the TX beam ID can be indicatedthrough a BCH, and the synchronization signals do not indicate the TXbeam IDs to be applied.

Subsequently, the controller 660 controls the modem 610 to generatesystem information and to generate a broadcast signal by encoding anddemodulating the sequence. According to one embodiment of the presentdisclosure, if the TX beam ID is indicated by the SCH, the broadcastsignal is not different for each TX beam but is identical for each TXbeam. Alternatively, according to another embodiment of the presentdisclosure, if the TX beam ID is indicated through the BCH, thebroadcast signal is different for each TX beam. Specifically, the TXbeam ID may be included as one information item of the systeminformation, or may be indicated in a form of a scrambling applied tothe system information. The system information can include informationfor reporting the number of TX beams supported by the BS so that theterminal can obtain frame synchronization.

The controller 660 controls the beamforming unit 640 to periodicallytransmit the synchronization signal and the broadcast signal and torepetitively transmit the synchronization signal and the broadcastsignal during one period such that the repetitively transmittedsynchronization signals and broadcast signals are beam-formed withdifferent TX beams. In other words, during one SCH/BCH period, thecontroller 660 transmits SCHs and BCHs, which are beam-formed withdifferent TX beams. In this situation, when the BS operates a pluralityof antenna areas in one cell, the controller 660 transmitssimultaneously the SCH and the BCH in the antenna areas. When the BSoperates a plurality of antenna areas, the BS includes a plurality of TXRF chains, or allocates antenna elements of the antenna array 650 to theplurality of antenna areas in a divided manner.

In addition, the controller 660 controls the receiver 620 to receive afeedback of a preferred TX beam ID from the terminal which receives theSCH and the BCH. The controller 660 recognizes a preferred TX beam ofthe terminal, and uses the preferred TX beam of the terminal whenperforming scheduling.

FIG. 7 is a block diagram illustrating a structure of a terminal in awireless communication system according to an embodiment of the presentdisclosure.

Referring to FIG. 7, the terminal includes an antenna array 710, abeamforming unit 720, a RX RF chain 730, a modem 740, a transmitter 750,and a controller 760.

The antenna array 710 is a group of antennas, and includes a pluralityof array elements. The beamforming unit 720 performs RX beamforming on asignal received through a plurality of antennas which constitute theantenna array 710. For example, the beamforming unit 720 includes aplurality of phase converters, a plurality of amplifiers, and a signaladder. That is, the beamforming unit 720 performs RX beamforming byregulating and adding phases of signals received through the respectiveantennas. The RX RF chain 730 converts an RF analog RX signal into abaseband digital signal. For example, the RX RF chain 730 can include anamplifier, a mixer, an oscillator, an Analog to Digital Converter (ADC),a filter, etc. Only one RX RF chain 730 is illustrated in FIG. 7.However, according to another embodiment of the present disclosure, theterminal can include a plurality of RX RF chains. In this situation, theterminal can simultaneously form a plurality of RX beams by the numberof RX RF chains.

The modem 740 performs a conversion function between a baseband signaland a bit-stream according to a physical layer standard of the system.For example, in an OFDM scheme, in a data transmission process, themodem 740 generates complex symbols by performing coding and modulationon a TX bit-stream, maps the complex symbols to subcarriers, and thenconfigures OFDM symbols by performing an IFFT operation and a CPinsertion operation. In addition, in a data reception process, the modem740 splits the baseband signal provided from the RX RF chain 730 on anOFDM symbol basis, restores signals mapped to the subcarriers by usingan FFT operation, and then restores a RX bit-stream by performingdemodulation and decoding. In particular, the modem 740 measures RXsignal strength for synchronization signals transmitted from a BS. Morespecifically, the modem 740 detects SCHs transmitted from the BS,measures RX signal strength for each SCH, and then provides the RXsignal strength to the controller 760.

The transmitter 750 converts a TX signal provided from the modem 740into a RF signal and then transmits the RF signal to the BS. Althoughnot shown specifically, the transmitter 750 includes a TX RF chain, anantenna, etc.

The controller 760 controls an overall function of the terminal. Forexample, the controller 760 generates a TX traffic packet and messageand provides it to the modem 740, and interprets a RX traffic packet andmessage provided from the modem 740. In particular, the controller 760provides control to determine preferred TX/RX beams by detecting a SCHand a BCH and to obtain synchronization and system information. Anoperation of the controller 760 for detecting the SCH and the BCH willbe described below.

The controller 760 determines a preferred TX beam and a preferred RXbeam by using SCHs transmitted from the BS. The controller 760 controlsthe beamforming unit 720 to change a RX beam in every period during aplurality of periods and to receive the SCHs, and thus acquires RXsignal strength for combinations of all of TX beams and RX beams.Accordingly, the controller 760 can determine one combination whichmaximizes RX signal strength as the preferred TX beam and the preferredRX beam. In this situation, the number of RX beams that can besimultaneously applied by the terminal may vary depending on the numberof RX RF chains included in the terminal. Further, the controller 760can feed back a TX beam ID of the preferred TX beam by using thetransmitter 750.

The controller 760 obtains at least one of a cell ID, an antenna areaID, and a TX beam ID by using the SCHs. A synchronization signalreceived through the SCH indicates the cell ID. When the BS operates aplurality of antenna areas in one cell, the synchronization signalfurther indicates the antenna area ID. In addition, according to oneembodiment of the present disclosure, the synchronization signals mayindicate TX beam IDs. That is, the controller 760 can identify at leastone of the cell ID, the antenna area ID, and the TX beam ID by using atleast one of the sequence of the synchronization signal detected by themodem 740, the position of the subcarrier to which the synchronizationsignal is mapped, the scrambling code for the detected synchronizationsignal, the covering code, etc. According to another embodiment of thepresent disclosure, the TX beam ID can be indicated by using the BCH. Inthis situation, the synchronization signals do not indicate the TX beamID to be applied.

The controller 760 controls the modem 740 to decode the BCH. The BCH ispaired with the SCH. The BCH is beam-formed with the same TX beam as theSCH paired with the BCH. Therefore, the modem 740 which detects thesynchronization signal determines a position of a BCH beam-formed withthe same TX beam from the synchronization signal, decodes the BCH, andprovides a decoding result of the BCH to the controller 760. Accordingto one embodiment of the present disclosure, if the TX beam ID isindicated by the SCH, the broadcast signal is not different for each TXbeam but is identical for each TX beam. Therefore, in this situation,the modem 740 can increase a decoding gain by combining signals receivedthrough a plurality of BCHs. Alternatively, according to anotherembodiment of the present disclosure, if the TX beam ID is indicatedthrough the BCH, the broadcast signal is different for each TX beam.Specifically, the TX beam ID may be included as one information item ofthe system information, or may be indicated in a form of a scramblingapplied to the system information. In this situation, the modem 740 canincrease a decoding gain by combining the signals received through theplurality of BCHs after performing descrambling.

The controller 760 obtains frame synchronization. That is, thecontroller 760 determines a boundary of a superframe, a frame, asubframe, etc., by using system information obtained through the BCH anda position of the detected synchronization signal. That is, thecontroller 760 determines a boundary of a SCH/BCH period by using thesystem information, and obtains the frame synchronization from theboundary. For example, if an end boundary of the SCH/BCH period has afixed position in the frame, the controller 760 determines the number ofSCHs by using the system information, determines the number of SCHslocated subsequent to the SCH detected by the terminal, determines theend boundary of the SCH/BCH period, and determines the boundary of theframe according to a positional relation of the end boundary and theframe. In this situation, if the position of the boundary of the SCH/BCHperiod on the frame is not pre-set, the controller 760 can obtaininformation for reporting the position of the boundary of the SCH/BCHperiod on the frame by using the system information.

The present disclosure provides a process for obtaining synchronizationby using a SCH and a BCH which are subjected to beamforming and forobtaining system information in a wireless communication system.Therefore, beamforming can be applied by using a process for obtaininginitial synchronization, thereby enabling effective communication.

Embodiments of the present invention according to the claims anddescription in the specification can be realized in the form ofhardware, software or a combination of hardware and software.

Such software may be stored in a computer readable storage medium. Thecomputer readable storage medium stores one or more programs (softwaremodules), the one or more programs comprising instructions, which whenexecuted by one or more processors in an electronic device, cause theelectronic device to perform methods of the present invention.

Such software may be stored in the form of volatile or non-volatilestorage such as, for example, a storage device like a ROM, whethererasable or rewritable or not, or in the farm of memory such as, forexample, RAM, memory chips, device or integrated circuits or on anoptically or magnetically readable medium such as, for example, a CD,DVD, magnetic disk or magnetic tape or the like. It will be appreciatedthat the storage devices and storage media are embodiments ofmachine-readable storage that are suitable for storing a program orprograms comprising instructions that, when executed, implementembodiments of the present invention. Embodiments provide a programcomprising code for implementing apparatus or a method as claimed in anyone of the claims of this specification and a machine-readable storagestoring such a program. Still further, such programs may be conveyedelectronically via any medium such as a communication signal carriedover a wired or wireless connection and embodiments suitably encompassthe same.

1. A method of operating a base station in a wireless communicationsystem, the method comprising: generating a synchronization signal to betransmitted through a Synchronization Channel (SCH); generating abroadcast signal to be transmitted through a Broadcast Channel (BCH);and transmitting repetitively the SCH and the BCH by performingbeamforming on the channels with different transmission beams.
 2. Themethod of claim 1, wherein the synchronization signal indicates at leastone of a cell identifier (ID) and a transmission beam ID applied to thesynchronization signal.
 3. The method of claim 2, wherein at least oneof the cell ID and the transmission beam ID applied to thesynchronization signal is indicated by using at least one of: a sequencewhich constitutes the synchronization signal, a position of a subcarrierto which the synchronization signal is mapped, a scrambling code for thesynchronization signal, and a covering code.
 4. The method of claim 1,wherein the broadcast signal indicates a transmission beam ID applied tothe broadcast signal.
 5. The method of claim 4, wherein the transmissionbeam ID is indicated by using at least one of an information itemincluded in the system information and a scrambling code applied to thesystem information.
 6. The method of claim 1, wherein the repetitivelytransmitting of the SCH and the BCH comprises: forming a transmissionbeam for a first antenna area by using a first antenna group among aplurality of antenna groups allocated respectively to a plurality ofantenna areas included in one cell; and forming a transmission beam fora second antenna area by using a second antenna group among theplurality of antenna groups.
 7. The method of claim 6, wherein therepetitively transmitting of the SCH and the BCH comprises formingsimultaneously a transmission beam for the first antenna area and atransmission beam for the second antenna area.
 8. The method of claim 6,wherein the synchronization signal indicates an antenna area ID of anantenna area corresponding to an antenna group which transmits thesynchronization signal.
 9. A method of operating a terminal in awireless communication system, the method comprising: detecting at leastone of Synchronization Channels (SCHs) repetitively transmitted by beingbeam-formed with different transmission beams; and obtaining systeminformation by using at least one of Broadcast Channels (BCHs)repetitively transmitted by being beam-formed with differenttransmission beams.
 10. The method of claim 9, wherein a synchronizationsignal received through the SCHs indicates at least one of a cell ID anda transmission beam ID applied to the synchronization signal.
 11. Themethod of claim 10, wherein at least one of the cell ID and thetransmission beam ID applied to the synchronization signal is indicatedby using at least one of: a sequence which constitutes thesynchronization signal, a position of a subcarrier to which thesynchronization signal is mapped, a scrambling code for thesynchronization signal, and a covering code.
 12. The method of claim 9,wherein a broadcast signal received through the BCH indicates atransmission beam ID applied to the broadcast signal.
 13. The method ofclaim 12, wherein the transmission beam ID is indicated by using atleast one of an information item included in the system information anda scrambling code applied to the system information.
 14. The method ofclaim 9, wherein the obtaining of the system information through atleast one of the BCHs comprises: combining broadcast signals receivedthrough at least two of the BCHs; and decoding the combined broadcastsignals.
 15. The method of claim 9, further comprising obtaining framesynchronization by using the system information.
 16. The method of claim15, wherein the obtaining of the frame synchronization comprises:determining a boundary of a period in which the SCHs and the BCHs arerepetitively transmitted by using the system information; anddetermining a boundary of the frame from the boundary of the period. 17.The method of claim 16, wherein the determining of the boundary of theperiod in which the SCHs and the BCHs are repetitively transmitted byusing the system information comprises: determining the number of SCHstransmitted from a base station by using the system information; andcalculating the number of SCHs located subsequent to the detected SCH byusing the number of transmission beams.
 18. The method of claim 9,wherein the detecting of the at least one of SCHs repetitivelytransmitted by being beam-formed with the different transmission beamscomprises: detecting SCHs which are beam-formed with the sametransmission beam by applying different reception beams; and determininga combination of a preferred transmission beam and a preferred receptionbeam which minimize reception signal strength.
 19. A base stationapparatus in a wireless communication system, the apparatus comprising:a modem configured to generate a synchronization signal to betransmitted through a Synchronization Channel (SCH) and generate abroadcast signal to be transmitted through a Broadcast Channel (BCH); abeamforming unit configured to perform beamforming on the SCH and theBCH with different transmission beams; and a controller configured totransmit repetitively the SCH and the BCH which are beam-formed with thedifferent transmission beams.
 20. The apparatus of claim 19, wherein thesynchronization signal indicates at least one of a cell ID and atransmission beam ID applied to the synchronization signal.
 21. Theapparatus of claim 20, wherein at least one of the cell ID and thetransmission beam ID applied to the synchronization signal is indicatedby using at least one of; a sequence which constitutes thesynchronization signal, a position of a subcarrier to which thesynchronization signal is mapped, a scrambling code for thesynchronization signal, and a covering code.
 22. The apparatus of claim19, wherein the broadcast signal indicates a transmission beam IDapplied to the broadcast signal.
 23. The apparatus of claim 22, whereinthe transmission beam ID is indicated by using at least one of aninformation item included in the system information and a scramblingcode applied to the system information.
 24. The apparatus of claim 19,wherein the controller is configured to form a transmission beam for afirst antenna area by using a first antenna group among a plurality ofantenna groups allocated respectively to a plurality of antenna areasincluded in one cell, and form a transmission beam for a second antennaarea by using a second antenna group among the plurality of antennagroups.
 25. The apparatus of claim 24, wherein the controller isconfigured to form simultaneously a transmission beam for the firstantenna area and a transmission beam for the second antenna area. 26.The apparatus of claim 24, wherein the synchronization signal indicatesan antenna area ID of an antenna area corresponding to an antenna groupwhich transmits the synchronization signal.
 27. A terminal apparatus ina wireless communication system, the apparatus comprising: a modemconfigured to detect at least one of Synchronization Channels (SCHs)repetitively transmitted by being beam-formed with differenttransmission beams; and a controller configured to obtain systeminformation by using at least one of Broadcast Channels (BCHs)repetitively transmitted by being beam-formed with differenttransmission beams.
 28. The apparatus of claim 27, wherein asynchronization signal received through the SCHs indicates at least oneof a cell ID and a transmission beam ID applied to the synchronizationsignal.
 29. The apparatus of claim 28, wherein at least one of the cellID and the transmission beam ID applied to the synchronization signal isindicated by using at least one of: a sequence which constitutes thesynchronization signal, a position of a subcarrier to which thesynchronization signal is mapped, a scrambling code for thesynchronization signal, and a covering code.
 30. The apparatus of claim27, wherein a broadcast signal received through the BCH indicates atransmission beam ID applied to the broadcast signal.
 31. The apparatusof claim 30, wherein the transmission beam ID is indicated by using atleast one of an information item included in the system information anda scrambling code applied to the system information.
 32. The apparatusof claim 27, wherein the modem is configured to combine broadcastsignals received through at least two of the BCHs, and decode thecombined broadcast signals.
 33. The apparatus of claim 27, wherein thecontroller is configured to obtain frame synchronization by using thesystem information.
 34. The apparatus of claim 33, wherein thecontroller is configured to determine a boundary of a period in whichthe SCHs and the BCHs are repetitively transmitted by using the systeminformation, and determine a boundary of the frame from the boundary ofthe period.
 35. The apparatus of claim 34, wherein the controller isconfigured to determine the number of SCHs transmitted from a basestation by using the system information, and calculate the number ofSCHs located subsequent to the detected SCH by using the number oftransmission beams.
 36. The apparatus of claim 27, further comprising abeamforming unit configured to apply different reception beams to SCHswhich are beam-formed with the same transmission beam, wherein thecontroller is configured to determine a combination of a preferredtransmission beam and a preferred reception beam which minimizereception signal strength.